The present invention relates to a magnetic tape cassette, and more particularly to a magnetic tape cassette of a type in which a loop of the magnetic tape is pulled out of the cassette for recording and playback.
Recently, very high recording densities have been achieved with magnetic tapes such as those used in VHS and .beta.-type magnetic tape cassettes (video cassettes).
Generally, in such magnetic tape cassettes the magnetic tape is pulled out of an opening provided in the front of the cassette to effect recording and playback More specifically, such a cassette has a guard panel angularly movable to open and close the opening. The guard panel closes the opening when the cassette is stored or not in use to prevent dust and the like from entering the cassette and also to protect the tape when the cassette is manually handled. At the time of recording and playback, the guard panel is moved to expose the opening, and a tape pulling member provided in the recording/playback apparatus is moved to the rear side (the nonmagnetic side) of the tape to suitably pull the magnetic tape out of the cassette through the front opening.
For example, as disclosed in Japanese Laid-Open (Kokai) Utility Model Applications Nos. 55-57184 and 58-141485, tape winding bodies around which a magnetic tape is wound have respective flanges each having a toothed outer periphery, and a reel brake is provided which engages the toothed portions to prevent accidental angular movement of the tape winding bodies during storage of the cassette to thereby eliminate loosening or jamming of the wound tape. The braking action of the reel brake is released by a brake release lever insertable into the cassette through a hole formed in the bottom wall of the cassette.
Referring to the above reel brake in further detail, the most common type includes a three-piece construction having engaging members engageable with respective ones of the flanges of the tape winding bodies and one release member which divides the action of the brake release lever into two parts transmitted to the respective engaging members.
Also, there has been previously proposed a reel brake of a two-piece construction which can achieve similar braking effects. FIGS. 1 and 2 are views explanatory of the above reel brake of the two-piece construction.
The reel brake 43 is in the form of an assembly composed of two brake member 45 and 50 fitted on a brake support shaft 44 projecting from a lower half case 3 of the cassette in such a manner that these brake members are pivotable about the brake support shaft. Engaging pawls 47 and 52 as well as operating extensions 48 and 53 are integrally formed with body portions 46 and 51, respectively, of the two brake members through which the support shaft 44 extends. The engaging pawls extend toward respective flanges 11a and 11b for engagement therewith, and the operating extension extend toward a hole 8 in which a brake release lever 30 is adapted to be inserted. The brake members 45 and 50 are normally urged by a torsion spring 55 so that the engaging pawls 47 and 50 are held in engagement with the corresponding flanges, with the operating extensions 48 and 53 held against each other to close the hole 8.
For releasing the braking, the brake release lever 30 is pressed against the operating extension 48 and 53 from below to space them apart in right and left directions (in directions indicated by arrows C in FIG. 1), so that the brake members 45 and 50 are angularly moved to disengage the engaging pawls 47 and 52 from gear portions 12a and 12b of the flanges 11a and 11b, respectively.
The operating extension 48 and 53 normally close the hole 8 and therefore also perform a dust-proofing function to prevent dust and the like from entering the cassette. To enhance the dust-proofing effect, it is preferred that the operating extensions 48 and 53 have respective planar slide surfaces extending substantially along the bottom surface of the cassette. On the other hand, it is also preferred that at least that surface of each of the operating extensions 48 and 53 facing the cassette bottom surface be inclined in order to easily produce component forces to push apart the operating extensions to the right and left when the operating extensions are pressed upon by the brake release lever 30. In general, the greater the angle of inclination the smaller the resistance to the insertion of the brake release lever becomes to enable a smooth brake sliding movement.
However, as is clear from the drawings, the greater angle of inclination of the operating extensions 48 and 53, the poorer the dust-proofing as a result of the presence of a gap between those portions facing the hole 8.
Thus, the above reel brake construction has been found to be not entirely satisfactory in that it must perform two contradictory functions, that is, the dust-proofing function and the brake sliding function.
On the other hand, as the demand for higher recording densities and higher-quality magnetic tapes increases, it becomes ever more desirable to provide a reliable cassette construction. Moreover, in order to compensate for dimensional inaccuracies in various members of the recording/playback device (e.g., dimensional inaccuracies of shafts supporting the rotatable reels), the reels are allowed to slightly move along the bottom surface of the cassette. Therefore, in the reel brake 43 shown in FIG. 1, as is clear from the drawings, when the reels are moved toward the hole to press against the engaging pawls 47 and 52, respectively, the body portions 47a and 52a are rotated so that a gap is formed between the operating extensions 48 and 53 which are disposed to close the hole 8. This is also a problem from the viewpoint of dust-proofing.
This problem is often encountered with conventional VHS-type cassettes. More specifically, the closure device for closing the hole (i.e., the operating extensions in the above example) is not directly urged in its closing direction, for example, by a spring, but indirectly urged in a direction to close the hole by the brake members having the engaging pawls. Therefore, when the positions of the brake members are changed in accordance with the movements of the reels, the above closure device is also influenced by such position change, so that a gap is formed between the closure device and the hole through which the insertion member is to be passed.